For example, measurements of contact lens powers are sometimes required in the product inspection during the manufacturing process of the contact lenses or in the fitting test thereof at the optometrist.
Conventionally, these lens power measurements of contact lenses have been conducted using a lens meter as described in Japanese Unexamined Patent Publication No. JP-A-5-126675 (Patent Document 1) in a state of supporting the contact lens with a proper jig.
However, the lens meter described in Patent Document 1 is the one that measures local lens powers based on the Hartmann method using four beams, which is only able to measure a single lens power at a time. For that reason, it is hard to obtain measurement results in a mapping display of lens powers that indicates where and how the lens powers are added to the optical part of the contact lens and so forth. Therefore, such lens meter is not suitable for measuring the power of contact lenses with different lens powers set in different regions such as the bifocal contact lens.
In recent years, some power measurement devices compatible with underwater use having a mapping display of lens powers are offered, for example under the product names of VC2001 and CONTEST by Visionix Limited and Rotlex Limited, respectively. However, the conventional underwater power measurement devices are made for measuring the lens power at each local measurement site and calculates the lens power from the focal distance determined for such site on the measuring optical axis. Therefore, in a glass lens that significantly varies the intersecting location of visual axes on the lens surface following the eyeball movements, the focal distance for each measurement site might have a certain significance, but it would be a different story for the contact lens fitted on the corneal surface that keeps the intersection of optical axes at nearly a constant location on the lens surface. In other words, it can be considered that the results of measurements by the conventional lens power measurement device for underwater use do not represent the power distribution of the contact lens with practically sufficient accuracy.